Disk lubricants use linear chain molecules made of a perfluoropolyether (PFPE) backbone, with a terminal functional group attached at both ends of the backbone. These lubricants are typically known as boundary lubricants. Boundary lubricants form a lubricating film when the functional groups of the lubricant attach to a surface being lubricated. Boundary lubricants, among other advantages, prevent solid to solid contact. If the backbone in a boundary lubricant molecule is long, the molecule tends to be heavier. A longer, heavier molecule provides the advantage of less evaporation while simultaneously providing the disadvantage of increasing free backbone length. On the other hand, if the molecule's backbone is short, the molecule tends to be lighter. A shorter, lighter molecule provides the advantage of lowering free backbone length while simultaneously providing the disadvantage of allowing greater evaporability. Lubricants, such as boundary lubricants, are used in many types of mechanical devices including disk drives and micro electronic mechanical systems. These devices typically include a moving part which is lubricated to prevent ware. The moving part moves relative to other parts of the device.
One problem that potentially arises with long molecular chains tethered on both ends by terminal functional groups attached to a substrate is that they still have multiple degrees of freedom that allow the middle of the chain to lift up from the disk surface (free backbone length), creating potential head/disk clearance issues. As a result, higher molecular weight lubricants, which would be preferred in a pure evaporation (Marchon, Karis, Dai, and Pit, IEEE Trans. Magn., vol. 39(5), pp. 2447. 2003) and dewetting (Waltman, Khurshudov and Tyndall, Tribology Letters, vol. 12, pp. 163, 2002) are detrimental to the overall head disk spacing margin (Khurshudov and Waltman, Tribology Letters, vol. 11, pp. 143, 2001). Hence, lowering molecular weight (MW) to get better clearance margin is only feasible to a certain point, as evaporation from the disk surface becomes increasingly problematic. In addition to these issues, decreased flying height tends to induce more severe slider/lubricant interactions (moguls, ripples, depletion), and as a result, there is a general trend towards higher lubricant-disk surface interactions as measured by lubricant bonding. Finally, in terms of total head/disk spacing, the lubricant thickness which used to be a negligible part of the budget can no longer be ignored. There is need for a robust lubricant system with a thickness in the 0.5-1.0 nm range. Prior to the invention, lubricant thicknesses were in 1.0-1.3 nm range.
Further, the article, Tribology Challenges for Head-Disk Interface Toward 1 Tb/in2 by Jing Gui (IEEE Transactions on Magnetics, Vol. 39, No. 2, March 2003), describes a Zdol as well as a Z lubricant. These lubricants are configured on a substrate in either a loop or train configuration respectively. However, these lubricants effectiveness are limited by use of terminal functional groups located at the ends of the lubricant backbone.